Temperature compensated oscillator driver

ABSTRACT

A circuit includes an oscillator having a driver and a resonator. The driver receives a supply voltage at a supply input and provides a drive output to drive the resonator to generate an oscillator output signal. A power converter receives an input voltage and generates the supply voltage to the supply input of the driver. A temperature tracking device in the power converter controls the voltage level of the supply voltage to the supply input of the driver based on temperature such that the supply voltage varies inversely to the temperature of the circuit.

TECHNICAL FIELD

This disclosure relates to integrated circuits and more particularly toa temperature compensated oscillator driver.

BACKGROUND

A wireless sensor network (WSN) (sometimes referred to as a wirelesssensor and actuator network (WSAN)) are spatially distributed autonomoussensors or nodes to monitor/control physical or environmental conditionssuch as temperature, sound, pressure and so forth. Sensors or actuatorson the network cooperatively pass collected data through the network toa central location where data is analyzed and stored and/or commandssent to operate the respective network nodes. Many networks arebi-directional, and thus also enable control of sensor activity. Thesenetworks and nodes are used in many industrial and consumer applicationssuch as industrial process monitoring and control, machine healthmonitoring, and so forth. One important factor for operating nodes onthe network is for very low power consumption.

Power consumption in such networks is an important factor as the devicesemployed at each node are relatively inexpensive and often times operatefrom battery power. One manner in which to reduce the power of low powerwireless networks is to have intermittent data transfer (burstoperation) when sending and receiving data to the nodes. Sleep timersare sometimes employed to synchronize the burst operations. Since thesleep timer is usually always ON, the sleep timer needs to be both verylow power and very accurate for lowest system power. However,conventional crystal oscillator drivers in the sleep timers have largetemperature variation and thus cause high power consumption at hightemperature which reduces battery lifetime.

SUMMARY

This disclosure relates to a temperature compensated oscillator driver.In one example, a circuit includes an oscillator having a driver and aresonator. The driver receives a supply voltage at a supply input andprovides a drive output to drive the resonator to generate an oscillatoroutput signal. A power converter receives an input voltage and generatesthe supply voltage to the supply input of the driver. A temperaturetracking device in the power converter controls the voltage level of thesupply voltage to the supply input of the driver based on temperaturesuch that the supply voltage varies inversely to the temperature of thecircuit.

In another example, a circuit includes an oscillator having a driver anda crystal resonator. The driver receives a supply voltage at a supplyinput and provides a drive output to drive the crystal resonator togenerate an oscillator output signal. A linear regulator receives aninput voltage and generates the supply voltage to the supply input ofthe driver. The linear regulator includes a pass transistor device toprovide the supply voltage to the supply input of the driver and aleakage current generating device to supply current to operate a gate ofthe pass transistor device. A temperature tracking device is operativelycoupled to the leakage current generating device and the gate of thepass transistor in the linear regulator. The temperature tracking devicecontrols the voltage level of the supply voltage to the supply input ofthe driver via the pass transistor device based on temperature such thatthe supply voltage varies inversely proportional to the temperature ofthe circuit.

In yet another example, an apparatus includes a remote sensor devicethat includes a radio circuit to communicate with the device via awireless network connection. The remote sensor device includes a timingcircuit to operate the device. The timing circuit includes an oscillatorhaving a driver and a crystal resonator. The driver receives a supplyvoltage at a supply input and provides a drive output to drive thecrystal resonator to generate an oscillator output signal. A powerconverter in the timing circuit receives an input voltage and generatesthe supply voltage to the supply input of the driver. A temperaturetracking device in the power converter controls the voltage level of thesupply voltage to the supply input of the driver based on temperaturesuch that the supply voltage input varies inversely proportional to thetemperature of the timing circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an example circuit that providestemperature compensation for an oscillator driver.

FIG. 2 illustrates a schematic block diagram of an example circuit thatprovides temperature compensation for a crystal oscillator driver.

FIG. 3 illustrates example power characteristics for a power converterthat provides temperature compensation for a crystal oscillator driver.

FIG. 4 illustrates a schematic diagram of a configurable power convertercircuit that provides temperature compensation for a crystal oscillatordriver.

FIG. 5 illustrates an example table of operating ranges for a circuitthat provides temperature compensation for a crystal oscillator driver.

FIG. 6 illustrates example operating power curves for a circuit thatprovides temperature compensation for a crystal oscillator driver.

FIG. 7 illustrates a block diagram of an example apparatus that providestemperature compensation for an oscillator driver in a remote sensordevice.

DETAILED DESCRIPTION

This disclosure relates to a temperature compensated oscillator driver.As temperature increases where oscillators (e.g., crystal oscillators)are employed, the respective driver circuits that operate in therespective oscillator circuits can experience a dramatic increase incurrent. Under such dynamic temperature conditions in conventionalcircuits, battery supply voltage supplying the driver can be reduced asthe current load increases. The temperature compensated driver asdescribed herein includes a power converter supplying voltage to thedriver that reduces the supply voltage provided to the driver astemperature increases to mitigate power increases in the driver.

In one example, a circuit includes an oscillator having a driver and aresonator. The driver receives a supply voltage at a supply input andprovides a drive output to drive the resonator to generate an oscillatoroutput signal. The power converter in turn receives an input voltage andgenerates the supply voltage to the supply input of the driver. Atemperature tracking device in the power converter controls the voltagelevel of the supply voltage to the supply input of the driver based ontemperature. The voltage is controlled to the driver such that thesupply voltage varies inversely to the circuit temperature (e.g., astemperature increases supply voltage decreases and vice versa). In thismanner, driver power is mitigated as temperature increases enablingbattery lifetime of circuits utilizing the oscillator and driver to beconserved. Various devices in the power converter can be selectivelyswitched to adjust the operating range (e.g., voltage and/or currentrange operations over temperature) of the converter. Substantially anypower converter can be employed that utilizes the temperature trackingdevice to reduce supply voltage based on temperature of the circuit asdescribed herein. These converters can include linear regulators,switched-capacitor supplies, and inductive-based switching supplies, forexample.

FIG. 1 illustrates an example circuit 100 that provides temperaturecompensation for an oscillator driver. As used herein, the term circuitcan include a collection of active and/or passive elements that performa circuit function, such as an analog circuit, digital circuit orcontrol circuit, for example. The term circuit can also include anintegrated circuit where all the circuit elements are fabricated on acommon substrate, for example. The circuit 100 includes an oscillator110 having a driver 130 and a resonator 132 (e.g., crystal resonator).The driver receives a supply voltage at a supply input 140 and providesa drive output 150 to drive the resonator 132 to generate an oscillatoroutput signal 114 at output 120. As shown, the drive output 150 drives asignal 154 to the resonator 132 where the signal 154 is out of phasewith the oscillator signal 114. The signal 114 is fed back to an input160 of the driver 130 where the driver operates as an inverter. A powerconverter 170 receives an input voltage and generates the supply voltageto the supply input 140 of the driver 130. A temperature tracking device180 in the power converter 170 controls the voltage level of the supplyvoltage to the supply input 140 of the driver 130 based on temperaturesuch that the supply voltage varies inversely to the temperature of thecircuit 100. Thus, as temperature of the circuit 100 increases, thetemperature tracking device 180 in the power converter 170 causes thesupply voltage to dynamically decrease the supply voltage to the supplyinput 140 of the driver 130. In this manner, power can be mitigated inthe circuit 100 since at lower values of supply voltage at input 140 thedriver 130 consumes less power.

In an example, the resonator 132 can be a crystal resonator, amicro-electromechanical system (MEMS) resonator, or an LC networkresonator however substantially any type of resonator circuit can beemployed.

The power converter 170 can be substantially any type of regulated powersupply that attempts to regulate a constant output supply voltage basedon a given input voltage. As temperature changes however, thetemperature tracking device 180 causes the supply voltage to the supplyinput 140 of the driver 130 to change to compensate for current changeswithin the driver due to changing temperature. The power converter 170can be a switched capacitor power supply in one example or aninductor-based switching power supply that receives the input voltageand generates the supply voltage to the supply input 140 of the driver130. In another example, the power converter 170 can be a linearregulator (e.g., low dropout regulator (LDO)) that receives the inputvoltage and generates the supply voltage to the supply input 140 of thedriver 130.

If a linear regulator is employed as the power converter 170, the linearregulator can include a pass transistor device (See e.g., FIG. 4) toprovide the supply voltage to the supply input 140 of the driver 130.The linear regulator can also include a leakage current generatingdevice to supply current to operate a gate of the pass transistordevice. In this configuration, gate leakage of the leakage currentgenerating device supplies current to the temperature tracking device180 to operate the gate of the pass transistor device. By using gateleakage to control current within the linear regulator, power in theregulator can further be conserved.

The temperature tracking device 180 can be a diode, a field effecttransistor device junction, or a bipolar transistor device junction thatvaries its voltage inversely proportional to the temperature applied tothe tracking device, for example. This variable voltage due totemperature is applied to the gate of the pass transistor device in thelinear regulator to control the supply voltage at the supply input 140of the driver 130. A programmable switching device (see e.g., FIG. 4)can be provided to adjust a range of current or voltage operations forthe power converter 170. The switching device can configure a number ofseries pass transistor devices, a number of series leakage currentgenerating devices, or a number of series or parallel temperaturetracking devices in the linear regulator to adjust the range of currentor voltage operations for the power converter 170.

FIG. 2 illustrates an example circuit 200 that provides temperaturecompensation for a crystal oscillator driver 210. The crystal oscillatordriver 210 (also referred to as driver) is an inverter and drives itsresistive output via resistor R1 to one leg of a crystal resonator 220.Another leg of the crystal resonator 220 is coupled to an input of thedriver 210. A resistor R2 may also be employed to promote oscillatorstability in the circuit 200. An input voltage shown as VDD drives apower converter 230 which provides a supply voltage LVDD (e.g., LocalVDD) to operate the driver 210. In one example, VDD may be greater than1 volts (e.g., 1.2 volts) and LVDD may be less than 1 volts (e.g., 0.5volts). As temperature changes across the circuit 200, a temperaturetracking device (TTD) 240 causes the voltage LVDD to change based ontemperature in order to mitigate power losses in the driver 210 asdescribed herein. The power converter 230 has some operatingcharacteristics that are provided as temperature changes and areillustrated in voltage diagrams depicted in FIG. 3.

FIG. 3 illustrates example power characteristics for a power converterthat provides temperature compensation for a crystal oscillator driveras described herein. One characteristic for the power converterdescribed herein is at any given temperature, to maintain asubstantially constant output voltage (LVDD) for a given input voltage(VDD). At 310, this relationship is shown where LVDD is illustrated onthe vertical axis and VDD is illustrated on the horizontal axis. Asshown, as VDD increases, LVDD is maintained at a substantially constantvoltage. At 320, LVDD change characteristics are plotted as temperaturechanges along the vertical axis. As shown at 320, as temperatureincreases, the temperature tracking device described herein causes LVDDto decrease (e.g., decrease in a substantially linear manner).

FIG. 4 illustrates a configurable power converter circuit 400 thatprovides temperature compensation for a crystal oscillator driver. Inthis circuit example, the crystal resonator and driver forming anoscillator described herein are represented as load current 410 forillustrative purposes. A linear regulator 420 operating as the powerconverter described herein receives an input voltage VDD and generatesthe supply voltage LVDD to the supply input of the driver (See e.g.,FIGS. 1 and 2). The linear regulator 420 includes a pass transistordevice 430 to provide the supply voltage LVDD to the supply input of thedriver represented as the current source 410. A capacitor C1 (orcapacitors) may also be present to filter LVDD. A leakage currentgenerating device 440 supplies current to a diode D1 to operate a gateof the pass transistor device 430. In this example, diode D1 operates asthe temperature tracking device described herein and is operativelycoupled to the leakage current generating device 440 and the gate of thepass transistor 430 in the linear regulator 420. The temperaturetracking device D1 controls the voltage level of the supply voltage LVDDto the supply input of the driver via the pass transistor device 430based on temperature such that the supply voltage LVDD varies inverselyproportional to the temperature. As the temperature of D1 increases, itsvoltage drop decreases and causes a decrease in LVDD via gate control ofthe pass transistor device 430.

In order to maintain the lowest power levels in the linear regulator420, gate leakage of the leakage current generating device 440 suppliescurrent to the temperature tracking device D1 to operate the gate of thepass transistor device 430. As noted previously, the temperaturetracking device D1 can be a diode such as in this example. Otherexamples include a field effect transistor device junction, or a bipolartransistor device junction that varies its voltage inverselyproportional to the temperature applied to the tracking device. Thisvariable voltage due to temperature is applied to the gate of the passtransistor device 430 to control the supply voltage LVDD.

A programmable switching device 450 can be employed to adjust a range ofcurrent or voltage operations for the linear regulator. The switchingdevice 450 can be programmed via factory setting commands, onsite usercommands, and/or via remote network control commands, for example. Theswitching device 450 can include user programmable switches that enableor disable one or more series and/or parallel devices in the linearregulator 420 to control the range of operations of the regulator.Disabling can include closing a switch that shorts a series devicewhereas enabling can include opening a switch to effectively insert theseries device into the circuit. For example, the switching device 450can configure a number of series pass transistor devices 430 or a numberof series leakage current generating devices 440 by enabling ordisabling control switches across the respective series devices.Programming can also include switching a number of series or paralleltemperature tracking devices to adjust the range of current or voltageoperations for the linear regulator 420.

FIG. 5 illustrates an example table 500 of operating ranges for acircuit that provides temperature compensation for a crystal oscillatordriver. As shown, for a given value of VDD and across temperature rangesof −40C to about 90C, current in the driver is maintained at arelatively constant value of about 11 nano amperes (nA) and power ismaintained at about 10.5 nano watts (nW). If VDD is increased to 1.2volts, the current in the converter is maintained at about 11 nA butpower increases to about 13 nW due to power conversion losses in thelinear regulator at higher values of VDD.

FIG. 6 illustrates example operating power curves for a circuit thatprovides temperature compensation for a crystal oscillator driver. Inthis example, conventional power curves 610 and 620 are shown wherepower is plotted on the vertical axis versus temperature on thehorizontal axis. Each of the conventional curves 610 and 620 illustratethat as temperature increases, power in the driver increases. When usingthe temperature tracking devices as described herein, the power curve630 can be provided which shows that as temperature increases, power inthe driver circuit is held substantially constant in the driver circuitover time due to altering the supply voltage to the driver based ontemperature as described herein.

FIG. 7 illustrates an example apparatus that provides temperaturecompensation for an oscillator driver in a remote sensor device 700. Theremote sensor device 700 (e.g., sensor, data collector, or controllableoutput device) includes a radio circuit 710 to communicate with thedevice via a wireless network connection. The remote sensor device 700includes a timing circuit 720 to operate the device. The timing circuit720 includes an oscillator having a driver 730 and a crystal resonator740. the driver 730 receives a supply voltage at a supply input 750 andprovides a drive output 754 to drive the crystal resonator 740 togenerate an oscillator output signal at output 756. A power converter760 in the timing circuit 720 receives an input voltage and generatesthe supply voltage to the supply input 750 of the driver 730. Atemperature tracking device 770 in the power converter 760 controls thevoltage level of the supply voltage to the supply input 750 of thedriver 730 based on temperature such that the supply voltage inputvaries inversely proportional to the temperature of the timing circuit720.

As noted previously, the power converter 760 can be a linear regulatorthat receives the input voltage and generates the supply voltage to thesupply input 750 of the driver 730. The linear regulator can include apass transistor device to provide the supply voltage to the supply input750 of the driver 730 and a leakage current generating device to supplycurrent to operate a gate of the pass transistor device. Gate leakage ofthe leakage current generating device can be employed to supply currentto the temperature tracking device 770 to operate the gate of the passtransistor device. The temperature tracking device 770 can be a diode, afield effect transistor device junction, or a bipolar transistor devicejunction that varies its voltage inversely proportional to thetemperature applied to the tracking device and the voltage is applied tothe gate of the pass transistor device to control the supply voltage. Aprogrammable switching device (See E.g., FIG. 4) can be provided toadjust a range of current or voltage operations for the power converter760.

What have been described above are examples. It is, of course, notpossible to describe every conceivable combination of components ormethodologies, but one of ordinary skill in the art will recognize thatmany further combinations and permutations are possible. Accordingly,the disclosure is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims. As used herein, the term“includes” means includes but not limited to, the term “including” meansincluding but not limited to. The term “based on” means based at leastin part on. Additionally, where the disclosure or claims recite “a,”“an,” “a first,” or “another” element, or the equivalent thereof, itshould be interpreted to include one or more than one such element,neither requiring nor excluding two or more such elements.

What is claimed is:
 1. A circuit, comprising: an oscillator having adriver and a resonator, the driver receiving a supply voltage at asupply input and providing a drive output to drive the resonator togenerate an oscillator output signal; a power converter that receives aninput voltage and generates the supply voltage to the supply input ofthe driver; and a temperature tracking device in the power converterthat controls the voltage level of the supply voltage to the supplyinput of the driver based on temperature such that the supply voltagevaries inversely to the temperature of the circuit.
 2. The circuit ofclaim 1, wherein the resonator is a crystal resonator, amicro-electromechanical system (MEMS) resonator, or an LC networkresonator.
 3. The circuit of claim 1, wherein the power converter is aswitched capacitor power supply or an inductor-based switching powersupply that receives the input voltage and generates the supply voltageto the supply input of the driver.
 4. The circuit of claim 1, whereinthe power converter is a linear regulator that receives the inputvoltage and generates the supply voltage to the supply input of thedriver.
 5. The circuit of claim 4, wherein the linear regulator includesa pass transistor device to provide the supply voltage to the supplyinput of the driver and a leakage current generating device to supplycurrent to operate a gate of the pass transistor device.
 6. The circuitof claim 5, wherein gate leakage of the leakage current generatingdevice supplies current to the temperature tracking device to operatethe gate of the pass transistor device.
 7. The circuit of claim 6,wherein the temperature tracking device is a diode, a field effecttransistor device junction, or a bipolar transistor device junction thatvaries its voltage inversely proportional to the temperature applied tothe tracking device and the voltage is applied to the gate of the passtransistor device to control the supply voltage.
 8. The circuit of claim4, further comprising a programmable switching device to adjust a rangeof current or voltage operations for the power converter.
 9. The circuitof claim 8, wherein the switching device configures a number of seriespass transistor devices, a number of series leakage current generatingdevices, or a number of series or parallel temperature tracking devicesto adjust the range of current or voltage operations for the powerconverter.
 10. A circuit, comprising: an oscillator having a driver anda crystal resonator, the driver receiving a supply voltage at a supplyinput and providing a drive output to drive the crystal resonator togenerate an oscillator output signal; a linear regulator that receivesan input voltage and generates the supply voltage to the supply input ofthe driver, the linear regulator includes a pass transistor device toprovide the supply voltage to the supply input of the driver and aleakage current generating device to supply current to operate a gate ofthe pass transistor device; and a temperature tracking deviceoperatively coupled to the leakage current generating device and thegate of the pass transistor device in the linear regulator to controlthe voltage level of the supply voltage to the supply input of thedriver via the pass transistor device based on temperature such that thesupply voltage varies inversely proportional to the temperature of thecircuit.
 11. The circuit of claim 10, wherein gate leakage of theleakage current generating device supplies current to the temperaturetracking device to operate the gate of the pass transistor device. 12.The circuit of claim 11, wherein the temperature tracking device is adiode, a field effect transistor device junction, or a bipolartransistor device junction that varies its voltage inverselyproportional to the temperature applied to the tracking device and thevoltage is applied to the gate of the pass transistor device to controlthe supply voltage.
 13. The circuit of claim 10, further comprising aprogrammable switching device to adjust a range of current or voltageoperations for the linear regulator.
 14. The circuit of claim 13,wherein the switching device configures a number of series passtransistor devices, a number of series leakage current generatingdevices, or a number of series or parallel temperature tracking devicesto adjust the range of current or voltage operations for the linearregulator.
 15. An apparatus, comprising: a remote sensor device thatincludes a radio circuit to communicate with the device via a wirelessnetwork connection, the remote sensor device includes a timing circuitto operate the device, the timing circuit comprising: an oscillatorhaving a driver and a crystal resonator, the driver receiving a supplyvoltage at a supply input and providing a drive output to drive thecrystal resonator to generate an oscillator output signal; a powerconverter that receives an input voltage and generates the supplyvoltage to the supply input of the driver; and a temperature trackingdevice in the power converter to control the voltage level of the supplyvoltage to the supply input of the driver based on temperature such thatthe supply voltage input varies inversely proportional to thetemperature of the timing circuit.
 16. The apparatus of claim 10,wherein the power converter is a linear regulator that receives theinput voltage and generates the supply voltage to the supply input ofthe driver.
 17. The apparatus of claim 16, wherein the linear regulatorincludes a pass transistor device to provide the supply voltage to thesupply input of the driver and a leakage current generating device tosupply current to operate a gate of the pass transistor device.
 18. Theapparatus of claim 17, wherein gate leakage of the leakage currentgenerating device supplies current to the temperature tracking device tooperate the gate of the pass transistor device.
 19. The apparatus ofclaim 18, wherein the temperature tracking device is a diode, a fieldeffect transistor device junction, or a bipolar transistor devicejunction that varies its voltage inversely proportional to thetemperature applied to the tracking device and the voltage is applied tothe gate of the pass transistor device to control the supply voltage.20. The apparatus of claim 19, further comprising a programmableswitching device to adjust a range of current or voltage operations forthe power converter.